Reducing power consumption of integrated circuits and systems continues to be a difficult but necessary task particularly for integrated circuits used in mobile devices such as laptop devices, handheld devices and other mobile and non-mobile devices. In addition, advances in technology create an increased demand for power consumption in order implement performance improvements afforded by the advances in technology. In many instances, the performance needs of applications implemented by the integrated circuits are variable depending on the context of the application. For example, integrated circuits used for communicating between a bridge circuit and a high speed I/O device such as a graphics processor, hard disk, network card, and/or other high speed I/O device can exploit periods of low demand for bandwidth to reduce power consumption.
A differential serial communication link having multiple lanes, such a PCI Express™ communication link or other suitable differential communication links, is particularly variable in terms of bandwidth demands required for the application. There are known methods for scaling the bandwidth through lane width sizing and/or powering down the differential serial communication link. However, for low bandwidth demands, the interface has to power up completely and run at a full clock rate before powering down after a period of inactivity. If the low bandwidth demands are frequent enough, the link may never have a chance to power down. It is therefore desirable to provide a method and apparatus to further reduce power consumption when bandwidth demands are low in a differential serial communication link.
In one method, power may be reduced on each active lane to multiple different power levels. As such, once the lane width has been determined after power on, the lane width stays the same but different power states may be used such as L0, which may be for example an 80 milliwatt mode, L0s which may be for example a 20 milliwatt mode, L1, which may be a 5 milliwatt mode and L2 or L3 which may be a mode that may consume less than 1 milliwatt of power. It would be desirable to provide further power savings in such systems.
Accordingly, a need exists for a method and apparatus to further reduce power consumption in connection with a differential serial communication link.